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RE: Too many connections?

Posted by chopper87@aol.com (A) on April 21, 2009 at 19:16:54

In Reply to: RE: Too many connections? posted by John Swenson on April 21, 2009 at 12:33:22:

John,

First, thank you for such thorough insight into the possible mechanics of this problem. I could almost simply answer yes to all of your inquiries because I have tried almost every conceavable combination of plugged, unplugged, power on and off.

First, my system consists of two tube amplifiers. One (a two watt 45 based SET Yamamoto amplifier) driving a pair of Lowther PM2MKII's, and the second one (a vintage Fisher SA-16 EL-84 amplifier configured for triode output) driving a pair of 12" Tone Tubby Alnico Hemp cone wide band drivers. These drivers are in open bafle configuration. There are a pair of powered corner loaded subwoofers as well.
Then I have the Sony XA77ES SACD/CD player and of course the MHDT Havana DAC. The Preamp is A Bent Audio dual transformer passive unit with two pairs of rca inputs and outputs with the two toggle switches choosing between them.
Interesting insight, (maybe), all of my electronics are equipped with three prong (grounding) plugs accept the vintage Fisher amplifier. I used to get shocked regularly by my previous Eico HF-86 amplifiers that were of similar vintage and also EL84 tube based as well as two prong AC.

Ok, the input switching between SPDIF and USB is audomatic within the DAC. There is no switch to choose which is active, the USB is always active when plugged in. So, there has been no need to choose. However I must always unplug the USB to try the SPDIF from the Sony or the PC.
The Havana and the Sony are always analog plugged to the passive preamp with two pairs of rca cables. This is where the pair of toggle switches comes in.
I have turned the PC and the DAC on and off when switching from USB to SPDIF and back again at the PC and DAC. Once the SPDIF is plugged into the PC and the Havana and the poer turned on, then there is always the buzz.
John, once I have initiated the BUZZZ, then I can physically remove the PC and the Havana from the room and the buzz remains. It remains until I connect the SPDIF from the Sony directly to the input of the Havana. At this point the USB is reconnected to the PC and the PC is turned on. I can then play music through the PC/Transport USB connection or the Sony SPDIF to Havana with NO buzz.
But, if I dare unplug and switch the SPDIF to the PC instead of the Sony (no matter if I power all down or not prior to this switch) The buz returns immediately and is everywhere until I start over again with only the Sony SPDIF to the Havana.

"Then you hooked the S/PDIF to the Sony. Did you turn anything off when" you did that? Was the USB to the computer still hooked up? Was the computer still on when connecting to the Sony?"

I'll have to give the above a shot in particular in the morning.

Thank you again for for your help. I did order a second mother board just to rule out a malfunction in the SPDIF section.

Lance A.





"That shock is the telltale here. Since the Havana is a tube DAC my guess is that there is something wrong with its output stage which is dumping high voltage on the output. This is NOT a good thing! You could damage your other equipment or YOU. Something could even catch on fire. Its serious.

At this point I would not hook the havana up to anything until it was replaced or fixed. Or at least checked out by someone who is familiar with debugging tube equipment if you don't feel up to the task.

It theoretically COULD be the power amp (is it tube by any chance?) but my guess is the Havana since the Havana is doing the input switching.

A few questions on what is happening: (don't try this again if you don't remember, at least until you knoe the Havana is safe)

So you have the havana turned on, the PC turned on, the havana analog out connected to the preamp. You have the havana connected to the USB port of the PC, is the S/PDIF cable also connected at this point? When you switch to the S/PDIF input are you just flipping a switch on the havana, flipping the switch then plugging in the cable or plugging in the cable then flipping the switch. What happens to the USB cable, do you leave it plugged in or unplug it? Do both the PC and havana stay turned on during this switch over? I hope you get the idea I'm trying to get a detailed list of what the initial conditions are (what is plugged in to what) and how the switch is made, and if any thing is turned on or off durring the switch.

Then you say you turn off the PC and the buzz remains. Did you leave the cables between the PC and havana plugged in? (was it just the S/PDIF or was the USB also connected?) At this point did you turn the havana off? If yes did it still buzz when turned back on? Was it still connected to the powered off computer?

You then tried connecting to the USB connection. Again did you unplug any cables or were they all still connected, just the switch on the havana being changed?

Then you hooked the S/PDIF to the Sony. Did you turn anything off when you did that? Was the USB to the computer still hooked up? Was the computer still on when connecting to the Sony?

Sorry about all the questions but when trying to debug such situations its important to know exactly the sequence of events.

John S."

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